This is a prevention intervention study for heterosexual HIV-discordant couples with an embedded observational substudy of biological factors that may reduce the risk of HIV-transmission. In the intervention trial high risk HIV-discordant couples are randomized into either a couple's intervention where each partner receives intensive HIV-risk reduction counseling, or an individual intervention which includes intensive counseling only for the infected partner. Couples are followed for one year. Outcomes include self-reported behavior change corroborated by biological markers including HIV, other STD's and pregnancy. The biological sub-study examines genetic, immunological and virological factors associated with the lack of HIV transmission in highly exposed seronegative women and their partners.